Add x11-fonts/bpmf-zihikai: Bopomofo IVS version of Zihi Kai Std font

The Bopomofo IVS fonts render a Han character together with its Bopomofo
reading, selected through Ideographic Variation Sequences and Private Use
Area code points. chinese/fcitx5-mcbopomofo 3.0 and later can emit such
text in its Bopomofo font annotation mode, which is aimed at educators and
publishers who need Bopomofo-annotated material.

The Han glyphs of this font are licensed under CC-BY 4.0 rather than the
SIL Open Font License 1.1 that covers the rest of the family.